US3837774A - Apparatus for molding rigid product from synthetic resinous material - Google Patents

Abstract

A machine operable to produce molded synthetic products in finished form in a continuous process, including mixing, pouring, molding, and curing the resultant product.

Description

United States Patent [1 1 Ross et al.

[451 Sept. 24, 1974 APPARATUS FOR MOLDING RIGID PRODUCT FROM SYNTHETIC RESINOUS MATERIAL [75] Inventors: Lee F. Ross, Los Gatos; James E.

Wilkinson; Fred A. Craig, both of San Jose; Allan M. Hudson, Mountain View, all of Calif.

[73] Assignee: Thiokol Corporation, Bristol, Pa.

[22] Filed: Dec. 1, 1972 [21] Appl. No.: 311,088

Related US. Application Data [62] Division of Ser. No. 107,174, Jan. 18 1971, Pat. No.

[52] US. Cl 425/144, 425/150, 425/164, 425/371, 425/817 C [51] Int. Cl. B29c 3/06 [58] Field of Search 425/4 C, 817 C, 371, 143,

[56] References Cited UNITED STATES PATENTS 3,017,662 l/l962 Marsh... 264/40 X 3,400,426 9/1968 Boggs 425/136 X 3,435,102 3/1969 Sullhofer 425/4 C X 3,601,854 8/1971 Trueblood 425/155 Primary Examiner-R. Spencer Annear Assistant Examiner-Mark Rosenbaum Attorney, Agent, or Firm--Thomas W. Brennan [57] ABSTRACT A machine operable to produce molded synthetic products in finished form in a continuous process, including mixing, pouring, molding, and curing the resultant product.

6 Claims, 21 Drawing Figures ELBQT, 774

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sum 1sur15 CONTROL WIRING IN SAW N.C. N.C. FARMER TRB-3 O- O TRB-4 PHOTO HEAD SWITCH SAFETY SWITCH CONTROL v 24| WARNER 103-4 0 H O lO3-6 TRAVEL TRB RELAY CLUTCH |59 No. 242 3 WARNER CUT-OFF |7-7 4/ g} o 17-9 HEAD sAw CLUTCH CONTROL FRAME SWITCH TRB RELAY No. 243 WARNER 17-? 45/ O I l7- 8 HEAD BRAKE k HEAD SWITCH J fir-Z95 APPARATUS FOR MOLDING RIGID PRODUCT FROM SYNTHETIC RESINOUS MATERIAL This is a divisional, of application Ser. No. 107174 filed Jan. I8, 1971 now US. Pat. No. 3,736,089.

BACKGROUND OF THE INVENTION As our natural resources such as wood become more and more scarce, and as labor costs increase in the lumber industry, the cost of natural building materials for the construction industry will increase to the point where synthetic products, which are conventionally milled from wood, may economically and to good structural advantage be produced through use of continuous mechanical processes using synthetic materials. Accordingly, it is one of the objects of the invention to provide an apparatus operable to produce continuously in elongate form any selected structural, non-structural or decorative member.

One of the difficulties that must be overcome when marketing a synthetic product, as opposed to a natural product, is the sales resistance that many people have toward a synthetic product. Accordingly, it is an advantage in marketing synthetic products that they resemble the natural product. Accordingly, it is another object of the present invention to provide an apparatus and method by which a product may be produced in a continuous process from synthetic materials, the finished product being susceptable of treatment to resemble the natural product.

Foam type synthetic materials, such as polyurethane foams have heretofore been produced in continuous processes, the end product usually being a substantial slab or bun of the expanded cellular synthetic product. United States Patents 3,296,658; 3,325,573; 3,354,503; 3,325,823; 3,475,522 and 3,476,845 teach different methods and apparatus for casting such expanded cellular synthetic resinous slabs or buns.

Other products have, of course, been manufactured from plastics. For instance, United States Patents 2,956,315 and 3,100,917 describe window and door frames fabricated from extruded plastic material. United States Patents 3,220,062 and 3,274,741 teach the manufacture of products fabricated from synthetic resinous material and used in the construction industry.

All of these patents, however, teach the use of an extrudable plastic compound formed into its ultimate configuration as a result of the extrusion process.

Still other patents, namely United States Patents 3,071,180; 3,178,768; 3,323,167; 3,408,690 and 3,422,178 teach methods and apparatus for forming articles from foamed polymeric materials such as expandable polystyrene beads. In general, these patents teach a process and apparatus permitting the charging of a mold with the polystyrene beads and the subsequent subjection of the beads to elevated temperatures as through the application of steam to effect expansion of the beads.

United States Patents 2,817,875 and 2,835,924 teach methods and apparatus for the continuous molding of flexible rubber foam latex strips such as might be used in the formation of flexible seals for refrigerator doors or weather stripping for automobiles and doors.

None of the patents noted above relate to the use of polyurethane type foam materials in the formation of the end product. The use of this type material and the product formed from such material in a continuous process is generally described in US. Pat.- Nos. 3,078,505, 3,254,464 and 3,265,786. In the first two of these latter patents, there is describedan end product that constitutes a lamination of a polyurethane type foam material with a more dense sheet material caused to adhere to the polyurethane foam to form a skin." As explained in Pat. No. 3,078,505, the skin coating material may be bonded to the foam body during manufacture. In Pat. No. 3,254,464, the interior of the panel described therein constitutes a rigid plastic foam with cover sheets intimately bonded thereto. So far as is known, synthetic foam materials have not been used to form rigid structural members having an exterior skin formed of the same material and in a continuous process. Accordingly, it is one of the objects of the invention to produce in a continuous process a foam product having a predetermined internal density such as to render the product rigid, while possessing an exterior skin" formed of the same material but of relatively greater density to provide a tough exterior surface.

So far as is known, apart from the present invention, apparatus has not been devised which may be used with many different types of curable liquid or foam type synthetic materials. Accordingly, another object of the invention is the provision of an apparatus and process suitable for use with any curable liquid or plastisol, for example, styrene polyester (with or without glass fibers), melamine formaldehyde, urea formaldehyde, polysulfide liquid polymers, curable silicone liquids, curable polybutadiene polymers, epoxy resins and other foaming systems such as foamed vinyls, foamed phenolics and foamed epoxy.

Another object of the invention is the provision of modular apparatus for continuously forming elongated rigid synthetic products.

In the continuous production of elongated rigid synthetic products, one of the problems is to secure separation of the product from the mold in which it is formed. Accordingly, it is another object of the invention to provide a method and means for insuring rapid and continuous separation of the product from the mold parts.

A problem frequently encountered in the continuous production of condensed foam materials into rigid structural members is the necessity to maintain the mold parts at a temperature such that the foam material contained within the mold will condense to the desired degree while curing to provide the requisite rigidity. Accordingly, it is a still further object of the invention to provide apparatus including movable endless mold parts capable of being heated and maintained at a predetermined temperature for a predetermined time to effect the curing of foam material contained within the mold at a predetermined pressure.

In a continuous production apparatus for the curing of synthetic materials, it is necessary that the mold belts forming the mold cavity be of substantial length so as to permit the material being cured to be confined for the requisite predetermined curing interval. The length of such belts makes it difficult to apply and remove the belts when it is desired to mold products of different configuration. Accordingly, it is a still further object of the invention to provide an apparatus constructed in a manner to permit the application and removal of the mold belts in an expeditious manner.

In the production of rigid elongated molded synthetic products, it is important that the mold parts be retained immovable with respect to each other for a considerable interval while the mold parts are moved along at a predetermined rate so as to confine the synthetic material in a mold cavity having constant volume during the curing process. To effect such control, the mold parts, when formed from adjacent reaches of endless mold belts, each comprising the complementary parts of a closed mold, are pressed together with constant pressure while being moved along during the curing process. Accordingly, it is a still further object of the invention to provide apparatus for retaining a pair of mold belts in juxtaposed clamped cavity-forming position over an extended length, and means for selectively varying the pressure upon the mold parts.

In the operation of a continuous process molding apparatus such as the one described herein, it is important that the apparatus have the capability of being converted to mold many difierent configurations from many different kinds of synthetic materials. Such versatility requires that appropriate control devices and circuits be incorporated which are susceptable of adjustment in correlation with the configuration and kind of material being run. Accordingly, it is a still further object of the invention to provide a continuous molding apparatus which incorporates the requisite controls to provide the versatility discussed.

Various types of plastic or synthetic resinous materials have been used to form laminated structures or products having a high degree of rigidity. So far as is known, foam type synthetic materials have not been used to form rigid structural configurations in the absence of a separate adherent skin. Accordingly, it is an important object of the present invention to provide a product constituted of condensed foam type synthetic material possessing a predetermined internal density of about 8 pounds per cubic foot and an integral skin" formed from the same material and having a density of about 12 pounds per cubic foot.

The invention possesses other objects and features of advantage, some of which, with the foregoing, will be apparent from the following description and the drawings. It is to be understood, however, that the invention is not limited to the embodiment illustrated and described as it may be embodied in various forms within the scope of the appended claims.

BRIEF SUMMARY OF THE INVENTION In terms of broad inclusion, the apparatus and method for forming elongated, rigid products from synthetic resinous material comprises apparatus for mixing and dispensing the constituent materials required to form the end product, an elongated modular framework upon which is rotatably disposed a continuous mold belt forming one-half of an elongated mold cavity, the other half of which is formed from a complementary elongated belt suitably supported on the frame for movement into and out of engagement with the other half of the mold belt to effect formation of the cavity. Heater means are provided in conjunction with the mold belts to maintain the temperature of the molds at a relatively constant level appropriate to the curing requirements of the synthetic resinous material being formed. Control means are also provided interconnected between the mixing and dispensing means, the heating means and the mechanical drive means of the mold to effect interruption of all processes if any one function of the machine is performed in a substandard manner.

With respect to the process by which foam material is caused to become a rigid structural member, rigidity of the final product is dependent upon density of the cured material, and density is dependent upon the quantity of constituents admitted to a mold cavity of predetermined crosssectional area, the rapidity and length of time that such material is permitted to expand and cure, and the pressure generated in the material during curing. Accordingly, the apparatus described hereinafter is designed to selectively optimize these conditions so that the ultimate product possesses the requisite density and rigidity.

DESCRIPTION OF DRAWINGS FIG. 1 is a schematic view in block diagram form il- Iustrating the mixing and dispensing equipment (dash lines) in conjunction with the molding and curing apparatus (full lines) and a cutoff mechanism and bundling and wrapping assembly, the latter two being shown in dash lines.

FIG. 1A is a schematic overall view showing in general the positional relationships of various of the major components of the apparatus. Legends have been applied for clarity.

FIG. 2A is a side elevational view of a portion of the input end of the molding and curing apparatus.

FIG. 2B is a continuation of the view illustrated in FIG. 2A and constitutes a side elevational view of an intermediate portion of the molding and curing apparatus.

FIG. 2C is a continuation of the view illustrated in FIG. 2B, and constitutes a side elevational view of the discharge end of the molding and curing apparatus.

FIG. 3 is an enlarged end elevation partly in vertical section taken in the plane indicated by the line 3-3 in FIG. 2C.

FIG. 4 is an enlarged fragmentary perspective view of a short section of the continuous chain assembly and chain guides, illustrating a mold belt guide block mounted on the chain assembly.

FIG. 5 is a vertical cross-sectional view of a pair of cooperating mold belts illustrating a pair of mold cavities and the guide ribs for guiding the mold belts.

FIG. 6 is a vertical cross-sectional view taken in the plane indicated by the line 6-6 in FIG. 7.

FIG. 7 is a side elevational view of the discharge end of the molding and curing apparatus from the side opposite the side shown in FIG. 2C and illustrating the single drive mechanism for upper and lower mold belts and associated guide chains. The guide chains are omitted from this view for clarity.

FIG. 8 is a vertical cross-sectional view through the apparatus taken in the plane indicated by the line 8-8 in FIG. 2C and illustrating the method of raising and lowering one mold belt and guide means therefor in relation to the other mold belt and guide means to effect separation of mold belts. Some of the structure is omitted for clarity.

FIG. 9 is a view similar to FIG. 8 but taken in the plane indicated by the line 9-9 in FIG. 2C.

FIG. 10 is an exploded view in perspective illustrating the details of construction of the elevator means for the auxiliary frame supporting one of the chain guides and mold belts.

FIG. 11 is an end elevational view partly in vertical section taken in the plane indicated by the line llll in FIG. 2A and illustrating the input end of the molding and curing apparatus. Portions of the structure are broken away to show the underlying structure.

FIG. 12 is a fragmentary elevational view in enlarged scale of the structure encompassed by the bracket 12 in FIG. 6.

FIG. 13A is a line-to-line schematic illustrating a portion of the control circuit for the apparatus.

FIG. 13B is a continuation of the line-to-line schematic illustrated in FIG. 13A and showing another portion of the control circuit.

FIG. 13C is a continuation of the line-to-line schematic illustrated in FIG. 13B.

FIG. 13D is the terminal end of the line-to-line schematic of the control circuit.

FIG. 13E is a schematic illustration of the control circuits controlling the cutoff mechanism at the discharge end of the apparatus.

FIG. 14 is a fragmentary perspective view illustrating a short length of the strip product produced by the apparatus.

DESCRIPTION OF PREFERRED EMBODIMENT Referring to the drawings, FIG. 1 illustrates schematically the molding and curing apparatus forming the subject matter of this invention, shown in full lines, in conjunction with mixing and dispensing apparatus, a cutoff mechanism and a bundling and wrapping device, the latter shown in broken lines since they form no part of the subject invention. FIGS. 2A, 2B and 2C illustrate in side elevation the entire length of the novel apparatus for continuously molding and curing a novel synthetic resinous product by a process believed to be novel.

The molding and curing apparatus includes a modular main frame assembly designated in its entirety by the numeral 2, and constituting the cooperative association of a modular input section 2a, a modular output section 2b, and modular intermediate sections 2c, 2d, 22, 2f and 2g. The modular construction indicated is desirable to lend versatility to the apparatus in handling different type materials requiring different cure times, enabling selective overall extension or contraction of the length of the apparatus by insertion or removal of intermediate sections.

The main frame assembly includes longitudinally spaced, vertically extending structural steel support standards 3a and 31; associated, respectively, with input and output sections 2a and 2b, each of the standards being provided with base pads 4 equipped with conventional leveling devices (not shown). Additional support standards 30, 3d, 3e, 3f and 3g are provided equally spaced between the support standards 3a and 3b. Each of the support standards is provided adjacent its lower end with a transversely extending cantilever beam 6, preferably having one end welded to the associated standard, and preferably formed from structural steel having a box cross section to provide the requisite rigidity. The free end of each cantilever beam is welded to a support plate 7 having a pad 7' at its lower end and projecting above the associated beam at its other end for purposes which will hereinafter be explained.

Between the top and bottom ends of the vertical standards, above each beam 6 and generally in planar alignment therewith, there is provided a second transversely extending cantilever beam 8, similar in construction to the beam 6, and where appropriate having approximately twice the depth to provide adequate rigidity.

To achieve a rigid modular construction, the transversely extending cantilever beams 8 on adjacent support standards are tied together by parallel longitudinally extending transversely spaced pairs of stringer beams 9 and 12 associated with frame section 2a, 9a and 12a associated with main frame section 2c, 9b and 12b associated with main frame section 2d, 9c and associated with main frame section 2e, 9d and 12d associated with main frame section 2f, and 9e and 12e associated with output section 2b.

Referring to FIG. 2A, it will there be seen that stringer beams 9 and 12, associated with the input section 2a, are welded in recesses formed in the associated cantilever beam 8 supported on standard 3a and project to the left of the vertical standard (as viewed in FIG. 2A) in a short cantilever extension. At their other ends the stringer beams 9 and 12 are provided with flat anchor flanges 13, adapted to be detachably anchored to the next adjacent main frame section 2c, including support standard 3C. Each of the pairs of stringer beams associated with each main frame section is in like manner welded to an associated support standard and detachably anchored to the next adjacent main frame section by a flange 13, thus enabling as many intermediate sections to be interposed in the structure as is desirable or necessary.

As shown in FIGS. 8 and 9, the pairs of stringer beams are spaced apart, the stringer beams 9 being next adjacent the associated vertical standard while the stringer beams 12 lie next adjacent the outboard ends of cantilever beams 8. It will thus be seen that the main frame assembly is rendered rigid and free standing by virtue of the interconnection of the cantilever beams by the longitudinal stringer beams.

Welded to the top surface of each of the longitudinally extending stringer beams is a generally rectangular bar 14 coextensive in length with each associated stringer. For purposes which will hereafter be explained in greater detail, each of the bars 14 is provided along opposite side edges with longitudinally extending chain rails 15 each of the chain guide rails being formed from appropriate bar stock and being adjustably mounted on the associated bar 14 so that the upper edge of each of the chain guide bar rails extends above the upper surface of the supporting bar.

Adjustability of the chain guide rails vertically with respect to the associated bar 14 is provided by an eccentric nut assembly designated generally by the numeral 16 and comprising a cap screw 17 threadedly engaged with the bar 14, and an eccentric bearing unit 18 rotatably disposed on the cap screw and rotatably adjustable in an elongated slot 19 formed in the rail to raise or lower the associated guide rail. Once the height of the upper edge of each guide rail has been adjusted to coincide with the upper edges of all the other associated chain guide rails the cap screws 17 are tightened to lock the eccentric unit in adjusted position. This construction is best shown in FIG. 4. Following adjustment of the separate chain guide rails, their top edges will lie in a common horizontal plane.

Supported on the main frame assembly is an auxiliary frame designated generally by the numeral 21. The auxiliary frame, like the main frame, is made up of joinable frame sections or modules 21a, 21b, 21c, 21d, 2le,

21 f, and 21g, correlated, respectively, to main frame sections 20, 2b, 2c, 2d, 2e, Zfand 2g. The entire auxiliary frame, once assembled, is supported in cantilever fashion for vertical movement in relation to the supporting main frame assembly and in relation to the underlying cantilever beams 8 and attached stringer beams.

The auxiliary frame comprises a series of axially spaced vertical support posts 22a, 22b, 22c, 22d, 22e, 22f and 22g, each having transversely extending lugs 23 and 23 projecting from opposite ends toward the associated vertical support standard 3 of the main frame assembly. Each pair of lugs is provided with vertically aligned apertures 24 and 24- to receive a vertical bearing shaft 26 fixedly supported at opposite ends on brackets 27 and 28, fixed to the associated vertical standard. As shown in FIG. 10, lug 23 is also provided with a second aperture 29 through which extends a ball bearing sleeve 31 adapted to work with ball spindle 32 to raise or lower the associated support post, which is guided in its movement by shaft 26. At its upper end, the ball spindle is rotatably journaled in bearing bracket 27 rigidly secured to the upper end of the associated main frame standard. Rotation of the spindle is effected by a drive collar 33 keyed to the spindle 32 and keyed also to the drive shaft 34 of a motor 35.

Each support post 22 is provided at its lower end with a transversely extending cantilever beam 36, the inboard end of which is rigidly welded to the vertical support post, while its outboard end is provided with a bifurcated latch bracket 37 for use in a manner which will hereinafter be explained. Extending longitudinally.

between the transversely extending cantilever beams 22 of the auxiliary frame 21, and associated with the separate auxiliary frame modules, are pairs of stringer beams: 38a-39a associated with the auxiliary frame section 21a, and 38b-39b associated with auxiliary frame section 213. Additional stringer beams 38c-39c, 38d-39d, 38e-39e, and 38f-39f are provided corresponding to the intermediate sections of the frame, each pair being welded at one end to one of the transversely extending beams 22, and the other ends having flanges 41 for detachable securement to the next adjacent section of the auxiliary frame.

After assembly of the auxiliary frame sections or modules, the transversely extending cantilever beams 22 and stringers 38-39 are positioned to overlie in planar alignment the corresponding underlying transversely extending beams 8 of the main frame and the stringer beams 9-12 associated therewith. As with beams 9-12, each of the beams 38-39 is provided with a longitudinally extending support bar 42 opposite side edges of each of which is provided with an adjustable chain guide rail 43 adjustable in the manner previously explained with regard to chain guide 15.

At the upper end of each vertical support post 22 of the auxiliary frame, there is provided a transversely extending cantilever beam 46 superimposed over and in planar alignment with beams 36, and provided with longitudinally extending angle bars 47 extending between the cantilever beams 46. It will thus be seen that the angle bars cooperate with cantilever beams 36 and 46 to form a very rigid auxiliary frame assembly which may be raised or lowered as a single unit in relation to the main frame assembly.

At one end of the main frame assembly there is provided axially extending pulley support brackets 48,

spaced transversely and welded at one end to the input end standard 3a of input section 21a as illustrated in FIG. 2A. The pulley brackets rotatably support a pulley 49 as shown. The pulley is adjustably supported on the support bracket by an appropriate take-up bearing as sembly, the adjustable spindle 50 of which is illustrated to the left of the pulley bracket in FIG. 2A.

With respect to this lower portion of the main frame assembly, a second pulley 51 is provided at the other or discharge end of the assembly, illustrated in FIG. 2C. As there shown, the pulley 51 is adjustably supported on an axially extending pulley support bracket 52 by an adjustable bearing assembly, the shaft 53 of which is illustrated to the right of the support bracket. The axis of rotation of pulleys 49 and 51 is correlated to the diameters of the pulleys so that the upper reach 54 of a mold belt 55 is disposed for rotation with the pulleys 49 and 51 will lie superimposed over and in axial alignment with the upper reach 56 of an endless chain assembly 57 movably supported along the chain guide rails 15, as illustrated in FIG. 4.

To effectively drive and guide each mold belt 55, each chain assembly is preferably fabricated from a pair of chain strands 58 and 58 interconnected by a series of guide blocks 59 having appropriately milled slots 61 therein adjacent opposite ends and adapted to wedgingly engage complementarily shaped resilient ribs 62 bonded to one side of a stainless steel ribbon 63 on the opposite side of which is bonded the resilient continuous strip 64 within which are formed mold cavities 66. i

As illustrated in FIG. 2A, the upper reaches 56 of the chain assemblies are rotatably disposed on sprockets 67 and 68 which change the direction of the chain assemblies to provide support for the lower reaches 69 which, together with the lower reaches 71 of the associated mold belts, are supported on rollers 72 provided for that purpose. At the discharge end of the apparatus (FIG. 2C), the lower reach of each chain assembly runs over a drive sprocket 76 keyed to a drive shaft 78, journaled in bearing 79 as shown. Appropriate tension is maintained in the pair of endless chain assemblies by takeup arms 81 (FIG. 2C) provided with sprockets 82 and adjustment spindles 83.

The auxiliary frame 21 is also provided with a pair of endless chain assemblies designated generally by the numeral 86, and rotatably supported at the input end of the apparatus on pairs of sprockets 87 and 88. At the discharge end of the apparatus the chain assemblies pass around appropriate drive sprockets 89. The drive sprockets 89 are keyed to drive shaft 91, which is in tum rotatably disposed on an appropriate bearing 92. Slack in the chain assemblies is taken up by adjustable take-up arms 93 journaled at one end to beams 386-396 and rotatably supporting at the other end appropriate sprockets 94 engaging the associated chain assemblies. Spindle 96 is provided to adjust the position of the take-up arms.

Referring to FIG. 2A, it will there be seen that the pairs of sprockets 87 and 88 are keyed to shafts journaled in bearings 93 and 94, respectively, the bearings being supported in turn on axially extending pulley support brackets 96 on which are mounted take-up bearing assemblies 97, the spindle of which may be rotated to adjust the position of pulleys 98 and 98. Pulleys 98 and 98 cooperating with the similar pulleys 99 and 99 at the discharge end of the apparatus, rotatably support

Claims (6)

1. Apparatus for continuously mixing, molding and curing synthetic resinous materials to produce a continuous elongated product therefrom comprising: a. mixing and dispensing apparatus for one or more chemicals in fluid form contained in a mixing chamber to produce a compound to be dispensed; b. molding and curing apparatus operatively associated with said mixing and dispensing apparatus to receive said compound as it is dispensed, said molding and curing apparatus including a pair of complementary mold belts arranged to form at least one mold cavity and into which said compound is dispensed and within which it is cured, said molding and curing apparatus including guide means for said mold belts, said guide means operatively associaed with said mold belts to form said cavity therebetween, means for driving the guide means associated with each of said mold belts at a speed substantially equal to the speed of said mold belts, heater means associated with each of said continuous mold belts to retain said mold belts at a predetermined temperature; and, c. means for monitoring the speed of said mold belts and operable to energize said heater means when said mold belts have attained a pre-determined speed.

2. The combination according to claim 1 further including automatic cutoff means connected to said molding and curing apparatus and adapted thereon to receive said elongated product from said mold belts to effect cutting of said continuous elongated product into strips of predetermined lengths.

3. The combination according to claim 2, in which control means are provided effective to control said mixing and dispensing means in correlation to operation of said molding and curing apparatus and automatic cutoff means whereby the entire apparatus is shut down if predetermined parameters for operation of the apparatus are not met.

4. The combination according to claim 3, in which said control means comprises a plurality of sequentially operable control circuits required to be activated in a predetermined order to effect activation of the apparatus.

5. The combination according to claim 3, in which said control means comprises a plurality of sequentially arranged control circuits interdependently associated to require activation in a predetermined sequence and including switch means in each control circuit whereby a failure in any given control circuit results in deactivation of all control circuits previous in sequence.

6. The combination according to claim 1, in which means are provided operatively associated with said heater means to sense the temperature of said mold belts and control energization of said heater means in response to said temperature.

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